Viscosity torsional vibration dampers exist in a variety of designs; similarly, various techniques are known for making such dampers. During manufacture, a housing body is generally formed which includes a working chamber for receiving a seismic ring and a viscous damping medium. A cover, which is connected to the housing body, e.g., by welding, following manufacture of the housing body, is provided as another component. The viscous working medium is introduced through an opening in the cover into the working chamber, containing an inserted seismic ring, and the opening in the cover is closed again when the working chamber is filled. In this manner, finished torsional vibration dampers are used in a number of ways to damp machine parts rotated by torsional vibration; e.g., they are screwed to a crankshaft to be damped or fastened to the crankshaft in some other manner.
To date, torsional vibration dampers of the aforementioned design and mode of operation were made of cast iron or rolled steel in deep-drawn or welded design, so that mechanical refinishing to produce the desired dimensions was necessary in every case. Furthermore, so-called hydroforming techniques were developed (U.S. Pat. No. 3,512,612), which, however, include rather crude tolerances and as a consequence the use of damping media of unusually high viscosity.
The development of modern work techniques, also applied, e.g., in the fabrication of coupling housings (U.S. Pat. No. 4,056,291) also led in the case of damper housings to methods of manufacture where housing bodies for torsional vibration dampers can be manufactured with extremely high accuracy by means of high speed metal forming machines (EU-A-O 302 283). The general feature of the manufacturing process using modern metal forming machines is the supposed elimination of costly refinishing work;in particular, very high productivity is said to be obtainable while maintaining the narrowest tolerances. Spinning or metal forming methods of this kind include the use of mandrel bodies (tensioning mandrel and spinning mandrel) between which the starting material is clamped as a round steel blank made of cold- rolled, killed steel sheet in a spinning lathe. On the spinning lathe the round steel blank is shaped into a deep pot, whereby the outer shell of the pot, which belongs to the shearing surfaces in the damper housing, is given a pre-polished, cold-hardened surface. On another pair of mandrel or core bodies, the pot shell is subsequently spun, thus worked, into the shape of the damper housing. Subsequently an abutment for the damper cover, which is connected in an oil-tight manner to the housing body by laser-beam welding, heat sealing or with sealing rings by means of spot welding, is molded on.
The foregoing process of manufacture requires at least the use of two pairs of mandrel bodies, if, starting from a round steel blank, a deep pot and from this subsequently the damper housing is spun or formed. The forming of the housing into the shape of the working chamber presupposes that the spinning rollers can change directions at least twice during forming; because of the tendency of the plate steel to spring back, this is problematic with respect to the demand for dimentionally accurate housing bodies.
Damper housings made by such a method (EU-A-O 302 283) have a structure in which the cover extends parallel to the radial inner attachment flange of the housing body and is connected to it, e.g., by welding. Both the cover and the attachment flange comprise aligned partial circles of bores receiving the attachment screws by means of which the damper is to be attached to a machine part to be damped.